1. Field of the Invention
The present invention relates to a lens-fitted photo film unit with an electronic flash device. More particularly, the present invention relates to a lens-fitted photo film unit with an electronic flash device with which daylight synchronization photography can be acceptably effected to take an exposure agreeably even for a rear light scene.
2. Description Related to the Prior Art
A lens-fitted photo film unit pre-loaded with unexposed photo film is widely used. Various ideas for lowering the cost of lens-fitted photo film units are known. In relation to exposure of each frame, the lens-fitted photo film unit has a construction including a fixed aperture stop and a shutter device of a fixed shutter speed. Also, a flash device in the lens-fitted photo film unit emits flash light at a fixed amount. It is likely that a photograph is taken in an underexposed or overexposed result due to lack of control of exposure according to types of scene to be photographed. It has been conceived to provide a lens-fitted photo film unit with an exposure control structure. It should be considered to minimize the rise in the manufacturing cost due to addition of the exposure control structure.
It is preferable in a lens-fitted photo film unit to automate control of exposure, as it should be handled easily even by unfamiliar users. To control the exposure, it is easier to change over the aperture stop than to change the shutter speed. JP-A 2001-083562 discloses an aperture stop device, which includes an aperture stop plate having a stop-down opening, and is changeable over between large and small aperture states by shifting the aperture stop plate. The aperture stop device, when in the large aperture state, sets a stationary stop opening effective, and when in the small aperture state, sets the stop-down opening effective.
If a principal object is located at a very near distance, flash light applied to the object has too high intensity, to create an overexposed state when the object is photographed. In the field of camera, a flash light amount control circuit is known, in which flash light reflected by the object is measured by a sensor, which quenches emission of the flash light when a value of integration of a current generated from the sensor comes up to a predetermined limit.
If a rear light scene is normally photographed, there occurs an underexposure in a principal object, which has lower brightness than a background. It is preferable to effect daylight synchronization photography, in which flash light is applied to a scene under daylight. However, the lens-fitted photo film unit with the stop changeable structure and flash adjusting structure is set in the small aperture state according to the high brightness from the background. A problem occurs in insufficiency in the effect of flash light. The underexposed state of the principal object cannot be prevented from occurrence. Also, the same problem arises in the construction of manually changing over the aperture stop and with the small aperture state designated.
In view of the foregoing problems, an object of the present invention is to provide a lens-fitted photo film unit with an electronic flash device with which a principal object can be photographed at an optimized exposure in daylight synchronization photography.
Another object of the present invention is to provide a lens-fitted photo film unit with an electronic flash device with which a flash light amount control circuit can be regulated to increase an amount of flash light in daylight synchronization photography.
In order to achieve the above and other objects and advantages of this invention, a lens-fitted photo film unit includes a flash emitter for emitting flash light toward a photographic object in flash photography. A flash amount control circuit quenches flash emission of the flash emitter when a value of integration of light reflected by the object in the flash photography comes up to a predetermined level, the light being measured by a first sensor. An aperture stop device designates one of a large aperture state and a small aperture state. Regulating means regulates operation of the flash amount control circuit in order to raise an amount of the flash light at a time of the flash photography when the small aperture state is designated.
The aperture stop device includes a stationary stop opening disposed in a photographic light path, a movable aperture stop plate shiftable into and out of the photographic light path, and a small-size stop-down opening formed in the movable aperture stop plate. The movable aperture stop plate is set away from the photographic light path if the large aperture state is designated, and is set in the photographic light path if the small aperture state is designated.
The aperture stop device further includes a second sensor for measuring brightness of the object. An aperture stop plate drive unit shifts the movable aperture stop plate according to the object brightness, so as to shift the movable aperture stop plate away from the photographic light path when the object brightness is low, and into the photographic light path when the object brightness is high.
The regulating means includes a switch, responsive to a signal from the aperture stop plate drive unit, for disabling the flash amount control circuit if the small aperture state is designated, and for enabling the flash amount control circuit if the large aperture state is designated.
The switch is a semiconductor switch, connected in series with the first sensor, being nonconductive if the small aperture state is designated, and being conductive if the large aperture state is designated.
In a preferred embodiment, furthermore, an externally operable mode selector designates a selected one of a flash off-mode, a first flash mode, and a second flash mode, to disable the flash emitter in designating the flash off-mode, to enable the flash emitter in designating the first or second flash mode, to set the movable aperture stop plate in the photographic light path in designating the first flash mode, and to set the movable aperture stop plate away from the photographic light path in designating the second flash mode.
The movable aperture stop plate is connected with the mode selector.
The regulating means includes a filter plate for moving according to the mode selector, the filter plate is disposed in front of the first sensor when the first flash mode is selected, and is disposed away from the first sensor when the second flash mode is selected.
In another preferred embodiment, the regulating means includes a switch, changed over by the mode selector, for disabling the flash amount control circuit when the first flash mode is selected, and for enabling the flash amount control circuit when the second flash mode is selected.
The switch is connected in series with the first sensor, is turned off when the first flash mode is selected, and is turned on when the second flash mode is selected.
Consequently, a principal object can be photographed at an optimized exposure in daylight synchronization photography, as the flash light amount control circuit is regulated to increase an amount of flash light in daylight synchronization photography, to emit flash light in full emission without quench according to designation of the small aperture state of the aperture stop.